"We know she's been prescribed Valium, plus the anti-anxiety pill Ativan," sources tell Showbizspy. "Mixed with Stattera for her ADHD, Topomax for migraines and Lithium for her bipolar disorder it's a wonder Brit even knows who she is any more."

One source claims Britney is "so stressed about the kids and so nervous about the tour that it's making her physically ill. The only way she can release that tension is to scream at whoever is closest."

"She locks herself in her room or the bathroom and frequently breaks down in tears."